1. Field of the Invention
The present invention relates to a ceramic composition by a composite stabilization process and by using waste materials including heavy metals for recycling the waste materials and a method for manufacturing the same, more particularly the present invention relates to the ceramic composition made from various waste materials such as an electric arc furnace (EAF) dust, a steel slag, an aluminum dross, a fly ash, a paper ash or other industrial dusts in order to utilize the ceramic composition for building materials or engineering materials and the method for manufacturing the ceramic composition.
2. Description of the Prior Art
Various waste materials generated from the industrial activities are generally divided into two groups. One group consists of specific waste materials which include hazardous elements and the other group consists of ordinary waste materials having little harmful elements.
Many heavy metals like iron (Fe), magnesium (Mg), titanium (Ti), lead (Pb), chrome (Cr), copper (Cu), nickel (Ni) or manganese (Mn). The heavy metals are erupted from the specific waste materials when the specific waste materials are buried in the ground according to an ordinary treating method, so fatal environment pollution may occur due to the heavy metals. Also, a cost and a reclaimed land for the waste materials become serious problems though the heavy metals are partially removed from the specific waste materials or the ordinary waste materials are buried in the ground. Therefore, a method for treating and recycling the waste materials is urgently demanded at present.
Hereinafter, several patents for recycling the waste materials will be mentioned as follows.
Japanese Patent No. 53-127,511 discloses one method for manufacturing a block by mixing an EAF dust with the conventional row materials. The block includes the EAF dust of 30 to 50 by weight percent and a sintering process is executed at a temperature of 630 to 830xc2x0 C. However, the block has a poor compressive strength of about 690 psi.
Another method for manufacturing a block is disclosed at U.S. Pat. No. 5,278,111 issued to Frame. The block contains an EAF dust of 30 to 60 by weight percent around the conventional row material after zinc (Zn) and lead (Pb) in the EAF dust are considerably volatilized through a calcination process. Though the block meets the permissible eruption limits of the heavy metals, the mechanical strength of the block decreases according as the amount of the EAF dust increases.
Also, a method for manufacturing a clinker is suggested at U.S. Pat. No. 5,672,146 issued to Aota et al. The clinker comprises an EAF dust and an alumina and heavy metals are hardly erupted from the clinker. The clinker is used as a row material to produce a tile or a block after it is grinded. The method, however, demands the milling process after a sintering step and the mechanical strength is not mentioned in that Patent.
As it is described above, those patents have the problem that the sintered bodies or the blocks have poor mechanical strength because homogeneous mixture is not formed during mixing the waste materials with the conventional row materials. Also, those patents mention only the specific waste materials except the ordinary waste materials such as the fly ash or the paper ash. Furthermore, a liquid phase excessively increases and the softening of the sintered body occurs since the main ingredients of the EAF dust likewise metals or metal oxides react with the conventional row materials such as a clay and they together form the liquid phase.
Therefore, in case of treating solid state waste materials having the hazardous heavy metals and the harmful ingredients, a treating and recycling method should be developed so as to manufacture a ceramic composition which has a high mechanical strength and can be available for various building materials or engineering materials by sufficiently mixing the ingredients of the waste materials while the heavy metals are not erupted from the ceramic composition.
Considering the above-mentioned problems, the present inventors have researched and developed a method for effectively treating and recycling waste materials having hazardous ingredients. As a result, the present inventors have accomplished a ceramic composition which can be available for a building material or an engineering material by a composite stabilization method without the eruption of hazardous heavy metals from the ceramic composition.
It is a first object of the present invention to provide a ceramic composition made from waste materials by a composite stabilization process in order to recycle waste materials such as an electric arc furnace dust, a steel slag, a fly ash, paper ash, an aluminum dross and so on.
It is a second object of the present invention to provide a method for manufacturing a ceramic composition made from waste materials by a composite stabilization process in order to recycle the waste materials.
To achieve the first object of the present invention, a ceramic composition comprises between about 5 and about 75 by weight part of a solid state waste material including heavy metals, between about 15 and about 45 by weight part of a fly ash and between about 5 and about 55 by weight part of a clay.
The solid state waste material is at least one selected from the group consisting of an electric arc furnace dust, a steel slag and a paper ash. Preferably, the ceramic composition further comprises between about 5 and about 15 by weight part of an aluminum dross.
According to one embodiment of the present invention, a ceramic composition comprises between about 5 and about 55 by weight part of an electric arc furnace dust, between about 15 and about 45 by weight part of a fly ash and between about 15 and about 55 by weight part of a clay. Preferably, the ceramic composition further comprises between about 5 and about 15 by weight part of a paper ash and the ceramic composition additionally comprises between about 5 and about 15 by weight part of an aluminum dross.
According to another embodiment of the present invention, a ceramic composition comprises between about 25 and about 40 by weight part of a fly ash, between about 15 and about 55 by weight part of a paper ash and between about 15 and about 50 by weight part of a clay.
According to other embodiment of the present invention, a ceramic composition comprises between about 15 and about 55 by weight part of a steel slag, between about 15 and about 45 by weight part of a fly ash, and between about 5 and about 45 by weight part of a clay. Preferably, the ceramic composition further comprises between about 15 and about 35 by weight part of an electric arc furnace dust or between about 15 and about 35 weight part of a paper ash.
Also, to achieve the second object of the present invention, a method for manufacturing a ceramic composition made from waste materials comprises the steps of:
a) forming a homogeneous slip by mixing a ceramic composition with a water wherein the ceramic composition comprises between about 5 and about 75 by weight part of a solid state waste material including heavy metals, between about 15 and about 45 by weight part of a fly ash and between about 5 and about 55 by weight part of a clay;
b) forming a shaped body having a predetermined shape by using said slip;
c) drying said shaped body; and
d) forming a sintered body by sintering said shaped body.
The step a) is performed after analyzing chemical constitutions of ingredients of the ceramic composition and measuring particle size distributions of the ingredients of the ceramic composition.
Preferably, the step a) is performed by primarily mixing an ingredient of said ceramic composition with a water considering volume ratios of particles having diameters of below about 10 xcexcm wherein the ingredient includes a volume ratio of the particles of 10 xcexcm which is larger than other ingredients of the ceramic composition and by mixing the ingredients with a water in the order of included particle sizes. More preferably, the step b) is performed by an extrusion method, an injection molding method or a pressing method.
According to one embodiment of the present invention the step a) further comprises sieving and milling the slip for homogeneously maintaining agglomerates in the slip and the milling is preferably performed by using a ball mill for about 1to about 5 hours.
The step c) is performed in a furnace at a temperature of about 40 to 60xc2x0 C. for a time of above 24 hours and the step d) is performed at a temperature of between about 900xc2x0 C. and about 1300xc2x0 C. for about 1to about 3 hours.
The ceramic composition of the present invention can be available for building or light construction materials such as a block, a tile or a retaining wall and be applied for a ceramic ware such as a porcelain or a sanitary arrangement. Also, the ceramic composition can be used for an engineering material such as a filter or a mechanical part.
As it is described above, the recycling method of waste materials is restrictedly available for cements though the treating method of the hazardous metals is partially developed centering around the recovery of the heavy metals from the waste materials or inhibiting the eruption of the heavy metals from the waste materials. That is, the recycling of the waste materials is restricted since several methods disclosed in the above patents do not simultaneously settle all the problems demanded for ceramic products such as the special characteristic, the mechanical strength and the lower manufacturing cost. Thus, it has not developed the ceramic composition having high mechanical strength and homogeneous characteristics by using the waste materials because the homogeneous mixture or the slip is hardly obtained when various waste materials having different chemical constitutions and characteristics are simultaneously treated.
Therefore, the present inventors have developed a method for forming a homogeneous and stable slip by mixing the waste materials considering the combinations, the average particle size distributions and the mixing order of the ingredients of the ceramic composition. The sintered bodies made from the stable slip have excellent mechanical strengths and beautiful appearances according to the present invention.
Since the heavy metals do not erupt from the sintered body in order to recycle the waste materials, the restraining mechanism for heavy metal eruption of the present invention will be described as follows.
During the heat treating the heavy metals and the metal oxides, an oxidation reaction of hazardous metals occurs and a eutectic reaction between the metal oxides also occurs. For example, the eutectic temperature of lead oxide (PbO) and silica (SiO2) is about 700xc2x0 C. and the liquid phase of the eutectic composition of PbO and SiO2 is formed above the eutectic temperature. When the eutectic reactions occur between various metals and metal oxides, the hazardous metals are fused into liquid phases of eutectic reactants, so the hazardous metals of the waste materials are stabilized. At the same time, the eutectic liquid phases and the fly ash together form retiary structure to accelerate the sintering of the shaped body of the waste materials. Therefore, the sintering process is performed at a relative temperature of between about 900xc2x0 C. and about 1200xc2x0 C. The hazardous metals are not exuded from the sintered body and the sintered body has a sufficient strength for the construction material or the engineering material.
In the meantime, the conventional ceramic products are generally manufactured by a ceramic composition consisting of a clay, a feldspar and a silica. The clay allows the mixture of the ceramic composition to have a plasticity and the feldspar forms a liquid phase during a sintering step. The silica forms a retiary structure to prevent a sintered body from softening during the sintering step.
According to the present invention, the waste materials include various metals and metal oxides as described above. Among the waste materials, solid state waste material such as the EAF dust, the steel slag or the paper ash forms a liquid phase during the sintering process, so the solid state waste material plays the part of the feldspar in the conventional ceramic composition. The solid state waste material contains heavy metals, in particular alkali metals and alkaline earth metals. The fly ash essentially consists of the silica and the alumina likewise the clay, however, the crystalline structure of the fly ash comprises the mullite and the cristobalite which are different from the alumina-silicate structure of the clay when the sintering process is performed at a temperature of above 1000xc2x0 C. Since the fly ash has characteristics quite different from the alumina-silicate structure, the fly ash has a little plasticity but has a high refractoriness though the chemical constitution of the fly ash is similar to the clay. Thus, the fly ash forms the retiary structure so that prevents the softening of the sintered body and increases the mechanical strength of the sintered body. That is, the fly ash plays the part of the silica in the conventional ceramic composition.
As it is described above, the feldspar-clay-silica system of the conventional ceramic composition can be substituted by the RO/R2O-clay-F/A system according to the present invention, so the ceramic composition of the present invention is manufactured on the basis of that fact. For manufacturing a ceramic product having a high mechanical strength by using the ceramic composition of the present invention, a combination of the ceramic composition having a proper RO/R2O-clay-F/A system is demanded through analyzing the chemical constitution and the crystalline structure of the ceramic composition. Though ceramic compositions are prepared from the same combinations of RO/R2O-clay-F/A, the sintered bodies respectively show different mechanical strengths and bulk specific gravities. Also, proper sintering time and temperature should be determined for each ceramic composition.
In the present invention, characteristics of the sintered body are determined by ceramic composition, mixing procedure, sintering temperature and sintering time. The sintered body meets the standard of heavy metal eruption tests, for example, toxic characteristic leaching procedure (TCLP) of the U.S. environment protection agency (EPA).
Table 1 shows the average weight percents of chemical elements contained in the ingredients of the ceramic composition according to the present invention.
In the table 1, the total* means the total amount of metal and metal oxide. Namely, Al2O3 represents the total amount of Al and Al2O3 and Fe2O3 represents the total amount of Fe, FeO and Fe2O3. The Ig-loss means decreased amounts due to volatile elements such as a water of crystallization, a hydroxide and a carbon dioxide during a heat treating process at a temperature of about 900 to 1000C. before analyzing the elements.